1. Field of the Invention
The present invention relates to a scroll type machine to be used as a compressor or an expander.
2. Prior Art
As a prior art example, a conventional scroll compressor will be described by referring to the accompanying drawings, especially FIGS. 12 and 13 of which the former is a vertical sectional view of the scroll type compressor and the latter is a sectional view taken along XIII--XIII of the former. As shown a sealed housing 8 is internally divided into a high-pressure chamber 44 and a low-pressure chamber 45 by a discharge cover 31. Within the low-pressure chamber there are provided at the upper and lower parts thereof, respectively, a scroll type compression mechanism C and a motor M which are coupled together through a rotary shaft 5 in an interlocking relationship with each other. The motor M comprises a rotor Ma and a stator Mb of which the former is fixed to a rotary shaft 5 and the latter is fixed to the sealed housing 8. The upper end of the rotary shaft 5 is supported by an upper bearing 71 provided on a frame 6 and the lower end thereof is supported by a lower bearing 72.
The scroll type compression mechanism C is provided with a stationary scroll 1 and a swivel scroll 2. The stationary scroll 1 is provided with an end plate 11, at the central part of which a discharge part 13 is provided, and a spiral wrap 12 erected on the internal surface of the end plate 11. The swivel scroll 2 is provided with an end plate 21 and a spiral wrap 22 erected on the internal surface of the end plate 21. Further, within a boss 23 erected on the outer surface of the end plate 21 there is rotatably received a drive bush 54 through a swivel bearing 73, and an eccentric pin 53 projecting from the upper end of the rotary shaft 5 is slidably fitted into a slide hole 55 drilled in the drive bush 54.
The stationary scroll 1 and the swivel scroll 2 are eccentric from each other by a predetermined amount so that when they are caused to mesh with each other as they are shifted by an angle of 180.degree., the side surfaces of the spiral wraps 12 and 22 are held in line-contact with each other at several points thereby providing a plurality of sealed spaces 24 therebetween. The swivel scroll 2 is slidably supported on the frame 6 fixed in the sealed housing 8, and between the swivel scroll 2 and the frame 6 there is arranged a rotation checking mechanism 3 comprising an Oldham's link or the like which, while allowing the revolutional motion of the swivel scroll 2, inhibits the rotation of the swivel scroll on its own axis.
Between two flanges 14 formed on the outer peripheral surface of the stationary scroll and four legs 6b projecting from an end plate 62 of the frame 6 there is arranged a ringlike support spring 32 made of a thin plate. As shown in FIG. 13, the support spring 32 is clamped to the flanges 14 by means of four bolts 36 and to the legs 6b by means of four bolts 37. Thus, the stationary scroll 1 is floatably supported on the frame 6 through the support spring 32 so that the stationary scroll can move vertically within a predetermined range and can incline within a predetermined angle.
On the rear surface of the end plate 11 of the stationary scroll 1 there are erected upright two concentric cylindrical flanges 15 and 16 which are concentric with the end plate 11. A cylindrical flange 38 projecting downward from the lower surface of the discharge cover 31 is sealingly and slidably fitted between the two cylindrical flanges 15 and 16 through U-shaped ringlike sealing members 74 and 75 which are respectively disposed in two gaps formed between the fitting surfaces of the flanges 15, 16 and 38 thereby forming an intermediate pressure chamber 40. The intermediate pressure chamber 40 is in communication with a sealed space 24 located midway in a gas compression passage through a lead hole 41 extending through the end plate 11. Further, on the inner peripheral side of the intermediate pressure chamber 40 there is formed a high-pressure chamber 42 and on the outer peripheral side thereof there is formed a low-pressure chamber 43.
In this type of compressor, when the motor M is driven, the swivel scroll 2 is driven by a swivel mechanism comprising the rotary shaft 5, the eccentric pin 53, the drive bush 54, the boss 23, etc. so that the swivel scroll 2 makes a circular orbit while it is hindered from rotating about its own axis. Then, with the motion of the swivel scroll, the gas enters the low-pressure chamber 45 through a gas intake pipe 82 and after passing along a path 61 between the sealed housing 8 and the end plate 62 of the frame 6, it is sucked into a sealed space 24 from the low-pressure chamber 43. Then, with a decrease in the volume of the sealed space 24 caused by the revolutional motion of the swivel scroll 2, the gas reaches the central portion of the machine as it is compressed, enters the high-pressure side 44 via the discharge port 13 provided at the center of the stationary scroll 1 and the high-pressure chamber 42 and is discharged outside through a discharge pipe 83.
In this case, a back pressure load based on the gas pressure in the high-pressure chamber 42 and the intermediate pressure chamber 40 is applied on the stationary scroll 1 so that the stationary scroll 1 is pressed against the swivel scroll 2 thereby preventing the leakage of the gas from within the sealed space 24. When a liquid is sucked into the sealed space 24, the stationary scroll 1 floats up through the support spring 32 to discharge the liquid thereby preventing the scroll type compression mechanism from getting damaged. Further, when the swivel scroll 2 inclines, the scroll 1 inclines through the support spring 32 so as to follow the scroll 2 so that both of the swivel scroll 2 and the stationary scroll 1 are prevented from being brought into partial contact with each other.
As described above, in the case of the conventional scroll type machine, the frame 6 is inserted into, and positioned properly in, the sealed housing 8 as shown in FIG. 14 and then fixed at a plurality of points on the outer periphery of the end plate 62 thereof by plug-welding W. Further, because the outer diameter of the frame 6 is somewhat smaller than the inner diameter of the sealed housing 8, a minute clearance .epsilon. is formed at the top of each of the four legs 6b. Consequently, the four legs 6b are considered to act as cantilever beams making the plug-welded points (i.e., the outer periphery of the end plate 62) their fulcrum points and therefore, during the operation of the compressor, the top ends of the legs 6b flex due to a compression force, centrifugal force and etc. Note that each of the legs 6b is set higher than a bottom surface 12a of the spiral wrap 12.
With the above structure, when the capacity of the compressor is large, the heights of the spiral wraps 12 and 22 tend to also be large and so will the height of each leg b. The amount of deflection of the top end of each leg 6b is proportional to the third power of the distance L (refer to FIG. 14) from the fulcrum so that the height of each leg 6b must be made increasingly large the larger the capacity of the compressor becomes.
When the top end of each of the legs 6b deflects, the stationary scroll 1 displaces horizontally through the support spring 32 whereupon the gaps between the fitting surfaces of the cylindrical flanges 15 and 16 projecting from the rear surface of the stationary scroll 1 and the cylindrical flange 38 projecting from the lower surface of the discharge cover change.
In the above case, there has hitherto been a problem in that although no difficulty takes place when the top end of each of the legs 6b deflects only a little and the above gaps change a little, if the deflection of the top end of each leg 6b is so large as to increase the gaps, an excessive compression load is repeatedly applied on the sealing members 74 and 75 disposed in the gaps resulting in damage to the sealing members.